I was thinking of the traditional OTL designs that parallel many tubes together. The Zana Deux you mention uses 6C33C-B power triodes to get that current output and costs $2200.00. Those kind of tubes were used as voltage regulators and power amps for servos, etc by the Russian military. So yeah, I stand corrected. You can get that much power out of a single tube. But, for that price you can get a good transformer coupled amp too.
When I mention that cheap iron can be quite good, I don't mean crappy transformers. There are transformers out there that are really good quality but only less expensive because they were made in quantity for another purpose, say a 70V speaker transformer or an SE guitar amp transformer. I've done experiments with 70V speaker transformers and have found them to work quite well in this, as well as other applications with the correct topology. Low distortion, super low output impedance (1 to 2 ohms) and flat response. Sounds great, too. I've built several.
If you go the traditional route and buy a purpose built output transformer from an 'audiophile approved' vendor, then expect to pay. If you want OTL and need to drive current hungry phones you need real power, which means big ass tubes or many tubes in parallel, so again, expect to pay.
The Decware amp mentioned as well as the Little Dot use a 'totem pole' or SEPP output. These can drive low impedances but not in the 16 to 32 ohm realm with any kind of current. The Decware claims an output impedance of around 60 ohms. Best to pair this with something in the 150 to 600 ohm range. The Little Dot's spec show that the power output diminishes the lower in impedance you go and the Decware would be the same due to similar topology. I haven't heard either of these amps; maybe they do a good job on low Z phones, but the numbers have me doubting they would do much for bass heavy music on inefficient headphones.
But, the original point about price seems to be true, those two examples are relatively inexpensive since they don't use trannys.
Edited by elliottstudio - 8/6/12 at 9:36pm